A2 upper with "f" marked front sight?

[dayman]

I'm planning on buying a new barrel for my AR.
After that happens I'll have nearly enough parts to build a second (in that, I've already put together a lower made largely from extra, or "upgraded" parts).
I've always liked the looks of the classic a2 upper, so I was thinking of going that way for a light weight truck gun. However, the barrel I'd be removing has a pinned "f" marked front sight.
Would this work, or should I just go with another flat top?
.04" doesn't seem like a lot, but I've been burnt by that attitude before.

The barrel is 16" with mid length gas.
I'm looking to use it pretty much exclusively inside 100yds.
I have a set of trijicon sights I'd be intending on using with it (so I can't really file them down).
I really don't want to deal with trying to pin a new base, or clamping something on over the holes.

 

[Bartholomew Roberts]

The F-marked front sight base just has a 0.40" higher shelf than an A2 front sight base. This is because using a detachable carry handle on top of a rail means you have to unscrew an A2 front sight post until it is almost hanging out of the A2 base.

Because you are mixing an A2 receiver with a F-marked base, you'll have the opposite issue - the sight post will just sit low between the ears. So you shouldn't have any problems zeroing.

 

[dayman]

cool, thanks.

I suppose I could also just get a flat top receiver and a detachable carry handle for about the same money as as a2 upper.
Then, if I decided to change things up I'd have that option.

 

[marine6680]

The extra height of the F marked front sight was added due to the shorter barrel of the m4.

If you have a shorter barrel and use the rifle length sight, you but the barrel at a steeper angle when aiming. So zeroing would be an issue, as you will not have enough travel to raise the sight post.

If you do the opposite and have a F marked sight and a rifle length barrel, you put the barrel angle too shallow when aiming. In that case, you may have the opposite issue, and not have enough downward travel. And even if you did, the post would be very low in the base.


Best to match the FSB to the barrel length you will use.

 

[Bartholomew Roberts]

The F-sight base is the same height as A2 sight. The difference is the shelf is 0.40" taller in order to allow you to raise the GI sight post enough to zero the M4 without having to have it dangling by the last thread as the Colt front sight post is only 0.27" tall.

Just to clarify, the barrel length has nothing to do with it. The old Colt XM177 uses the same front sight base as the M16A1. Same with the Colt SP1 Carbine. Civilian A2-style carbines from the factory will also use an A2 front sight post despite having a 16" barrel.

Likewise, the M16A4 (flattop) uses an F-marked front sight base, the same as the M4.

Using an F-marked front sight base with an A2 upper will just mean you have to crank the front sight post down into the base deeper.

I suppose I could also just get a flat top receiver and a detachable carry handle for about the same money as as a2 upper.
Then, if I decided to change things up I'd have that option.

Personally, I'd go that route even if all I wanted to do is shoot iron sights. With a flattop, you can put M1A style National Match sights on an AR, H&K drum sights, and a dozen different iron sight variations never seen before on any other rifle. If you go with an A2 upper, then you are stuck with A2 sights - and they are great sights; but your options are limited.